The molecular analysis of gene expression in insects, with the notable exception of Drosophila melanogaster, lags behind those in prokaryotes, yeast, and vertebrates. A well characterized insect system amenable to dissection at the molecular level is provided by the antibacterial response of lepidopteran insects. Resistance to infection in insects is accomplished largely via structural barriers that limit access to the hemocoel. If these structural barriers are disrupted via injury or attack, potential pathogens or parasites may gain access to the hemocoel. To survive these infections, insects have evolved a set of active secondary defenses that (i) limit hemolymph loss and heal wounds, (ii) detect and eliminate invaders, and (iii) protect the injured host while structural barriers and depleted defenses are restored. One component of the active defensive arsenal against bacteria is the regulated synthesis of antibacterial, hemolymph proteins. The long term goal of the proposed research is to discover molecular mechanisms regulating the expression of genes encoding insect antibacterial proteins. The present proposal focuses on transcriptional regulation of antibacterial protein genes, gene structure, and tissue specific expression. Specific objectives are: (1) to determine the contribution of transcriptional control to peptidoglycan regulation of fat body cecropin-like protein (CLP) and attacin-like protein (ALP) synthesis; (2) to isolate and characterize M. sexta genes encoding CLP and ALP; (3) to analyze secondary structural elements associated with CLP and ALP genes in naive and peptidoglycan-induced fat body; and (4) to determine whether established lepidopteran cell lines exhibit enhanced transcription from antibacterial protein genes and synthesize elevated levels of CLP and ALP in response to peptidoglycan elicitors. The proposed research will yield new information concerning (i) the insect host-pathogen/parasite interaction and (ii) the structure and regulation of insect genes. This knowledge may contribute to the management of insect vectors of human and animal disease.